1. Field of the Invention
The invention relates to a two-stage pressure atomizer nozzle according to the preamble of claim 1, which is used, for example, in the premix burners of a gas-turbine plant.
2. Discussion of Background
With the increasing operating pressures of modern gas turbines, good distribution of the liquid fuel is becoming more and more of a problem. The reasons for this lie mainly in the increasing air density and in its impulse, which have a greater effect on the distribution of the fuel droplets.
EP 0 794 383 A2 has a two-stage pressure atomizer nozzle which enables the droplet spray to be adapted to the respective load conditions with regard to the atomization quality, the droplet size and the spray angle. Furthermore, the nozzle is distinguished by a simple type of construction requiring only a little space. To this end, it comprises a nozzle body having a turbulence and/or swirl chamber formed in the interior and connected to an exterior space via a nozzle bore. In addition, the pressure atomizer nozzle has at least one first passage for the liquid to be atomized, through which the latter can be fed under pressure. At least one further passage for a portion of the liquid to be atomized or for a second liquid to be atomized leads into the turbulence and/or swirl chamber, through which passage said portion of the liquid or the second liquid can be fed under pressure and with a swirl.
However, it has been found that, with increasing size of the burners, i.e. in the case of development as can clearly be seen when comparing FIGS. 12 and 17 of EP 0 794 383 A2, it becomes more difficult to ensure a uniform fuel distribution, even when using such a two-stage pressure atomizer nozzle. This can be attributed both to the overriding effect of the air on the distribution of the fuel droplets and to the increasing diameter of the burners or to the opening angle of their swirl generators.
The air which flows around the central fuel nozzle of such a large burner remains mainly in the region of the burner axis. If virtually the entire fuel quantity can be carried by this air, a center enriched with fuel results, in which case no large liquid-fuel quantities can pass into the outer region. Therefore the main vaporization of the fuel often already takes place before the fuel droplets reach the desired points of the burner, i.e. its outer regions. Thus high NOx emissions and a flashback of the flame may be caused in this case.
In order to also realize spraying of the fuel droplets into the outer regions of the burner, swirl nozzles having large jet angles are often used. Although such a swirl nozzle sprays in the correct direction, the small droplets produced by it do not have a sufficient impulse to transport the liquid fuel into the outer regions of the burner before the liquid fuel is vaporized or affected by the air. On the other hand, on account of the large spread during the initial distribution of the droplet sizes, large droplets may pass into the outer regions. However, these droplets are not vaporized and may finally impinge on the burner walls, with the risk of the flashback of the flame into the flow regions near the walls.
On the other hand, if a turbulence-intensified fuel jet, disclosed, for example, by EP 0 794 383 A2, is utilized, this fuel jet produces large droplets, having a sufficiently high impulse to pass through the air zone. However, these jets have a small spread angle and do not cause the droplets to be uniformly distributed in all directions.